[Bug c++/100617] New: [modules] Exported namespace not visible from outside when the module imports another module that declares the same namespace

["amorvincitomnia.iw at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100617

            Bug ID: 100617
           Summary: [modules] Exported namespace not visible from outside
                    when the module imports another module that declares
                    the same namespace
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amorvincitomnia.iw at gmail dot com
  Target Milestone: ---

See it live: https://wandbox.org/permlink/1Tgk83eCk7VYm3a3


Minimum code to reproduce the error:

//test2.cc
export module test2;
export namespace A{}

//test1.cc
export module test1;
import test2;
export namespace A{
    int a = 3;
}

//prog.cc
import test1;

void g(){
    A::a;
}



Compile it with:

$ g++ "-std=c++20" "-fmodules-ts" "test2.cc" "test1.cc" "prog.cc"



Results in error:

prog.cc: In function 'void g()':
prog.cc:5:5: error: 'A' has not been declared
    5 |     A::a;
      |     ^



Reproduces in both g++ 11.1.0 and g++ 12.0.0 20210510.